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2 £0                                         TAPIRS                                          CHAP.
Ungulate Pheneteodu-s (see p. 202). In the next stage (an
embryo of 25 mm.) the humerus has slightly decreased in pro-
portionate length, and has come to be more like that of
IRpparion. In both of these embryos it should be noted that
the ulna is complete and separate from the radius. In the
second of the two it has more distinctly acquired the form which
it will possess in the adult. The second metacarpai—one of the
splint bones of the adult—is tipped with a small nodule of
cartilage, which is clearly the representative of one or more of the
phalanges belonging to that digit.
Fazn. 2. Tapiridae.—The Tapirs may be distinguished from
the Horse and from the Rhinoceros tribe by a few characters,
which are as follows :---
The dentition is generally the full one of forty-four teeth.
The premolars in the more ancient forms are unlike the molars,
but like them in more recent forms. The molars of the upper
jaw have two crests parallel and united by an outer crest. The
fore-feet have four, the hind-feet three toes.
The family is fully as ancient as that of the Equidae, but the
specialisation of the toes never advances so far. The modern
representatives of the order are, so far as the feet are concerned,
in the condition of very early representatives of the equine stock.
Nor do the teeth of the Tapirs ever reach the complicated pattern
of that presented by at least the modern Horses, or indeed of the
Palaeotheres. Apart from this it is not an easy matter to dis-
tinguish accurately between these several families, including the
Lophiodontidae, which, as already mentioned, is placed nearer to
the Tapiridae than to the Palaeotheriidae. Indeed the differentia-
tion of these two families, the Tapiridae and the Lophiodontidae,
seems to be a matter of the greatest difficulty. The difficulty is
well emphasised by the fact that naturalists disagree most
profoundly as to the relations of various genera of extinct Tapir-
like animals. For Mr. Lydekker the genus JLopJiiodon includes
also the American genera IsectolopJius and fSystemodon, which are
placed t>y Zittel in the sub-family Tapirinae as opposed to
Lophiodontinae, which contains Zophiodon and JEfelcdetes. The
existing Tapirs can be differentiated from the existing Horses with
great ease, as the following account of the existing genera will
genus   Tapims is  now met with only in   South   and